High Velocity Clouds: Building Blocks of the Local Group

Abstract

We suggest that the high--velocity clouds (HVCs) are large clouds, with typical diameters of 25 kpc and containing 5e7 solar masses of neutral gas and 3e8 solar masses of dark matter, falling onto the Local Group; altogether the HVCs contain 10${}^{11}$ solar masses of neutral gas. Our reexamination of the Local-Group hypothesis for the HVCs connects their properties to the hierarchical structure formation scenario and to the gas seen in absorbtion towards quasars. We begin by showing that at least one HVC complex (besides the Magellanic Stream) must be extragalactic at a distance > 40 kpc from the Galactic center, with a diameter > 20 kpc and a mass > 1e8 solar masses. We interpret the more distant HVCs as dark matter ``mini--halos'' moving along filaments towards the Local Group. Most poor galaxy groups should contain HI structures to large distances bound to the group. The HVCs are local analogues of the Lyman--limit clouds We argue that there is a Galactic fountain in the Milky Way, but that the fountain does not explain the origin of the HVCs. Our analysis of the HI data leads to the detection of a vertical infall of low-velocity gas towards the plane. This implies that the chemical evolution of the Galactic disk is governed by episodic infall of metal-poor HVC gas that only slowly mixes with the rest of the interstellar medium. The Local--Group infall hypothesis makes a number of testable predictions. The HVCs should have sub-solar metallicities. Their H$\alpha$ emission should be less than that seen from the Magellanic Stream. The clouds should not be seen in absorption to nearby stars. The clouds should be detectable in both emission and absorption around other groups.

65 pages, 27 figures (26 postscript, 1 gif). Submitted to Astrophysical Journal Full figures and paper available at http://www.astro.princeton.edu/~dns/

References in corpus (7)

• Iron as a tracer in galaxy clusters and groups
• The HI Mass Function of Galaxies from a Deep Survey in the 21cm Line
• The Metallicity and Dust Content of HVC 287.5+22.5+240: Evidence for a Magellanic Clouds Origin
• WHAM Observations of H-alpha Emission from High Velocity Clouds in the M, A, and C Complexes
• The Smith Cloud: HI associated with the Sgr dwarf?
• The Delayed Formation of Dwarf Galaxies
• MCG+00-32-16: An Irregular Galaxy Close to the Lowest Redshift Absorber on the 3C 273 Line of Sight

Cited by in corpus (262)

• Dark Matter Substructure in Galactic Halos
• Where are the missing galactic satellites?
• Observational evidence for self-interacting cold dark matter
• Small-Scale Challenges to the $\Lambda$CDM Paradigm
• The New Galaxy: Signatures of its Formation
• Baryons in the Warm-Hot Intergalactic Medium
• The Origin of Star Formation Gradients in Rich Galaxy Clusters
• The tumultuous lives of galactic dwarfs and the missing satellites problem
• Cold gas accretion in galaxies
• Gaseous Galaxy Halos
• Highly-Ionized High-Velocity Gas in the Vicinity of the Galaxy
• Multi-Phase Galaxy Formation: High Velocity Clouds and the Missing Baryon Problem
• The Wisconsin H-Alpha Mapper Northern Sky Survey
• Halo Properties in Cosmological Simulations of Self-Interacting Cold Dark Matter
• The Metamorphosis of Tidally Stirred Dwarf Galaxies
• Compound gravitational lensing as a probe of dark matter substructure within galaxy halos
• Distances and Metallicities of High- and Intermediate-Velocity Clouds
• Passive spiral formation from halo gas starvation: Gradual transformation into S0s
• ELVIS: Exploring the Local Volume in Simulations
• Accretion-Driven Turbulence as Universal Process: Galaxies, Molecular Clouds, and Protostellar Disks
• The Magellanic Stream, High-Velocity Clouds and the Sculptor Group
• X-ray Properties of Groups of Galaxies
• Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy
• Uncovering CDM halo substructure with tidal streams
• Probing Galactic Halos with Fast Radio Bursts
• Star formation sustained by gas accretion
• Probing Dark Matter Substructure in Lens Galaxies
• HIPASS High-Velocity Clouds: Properties of the Compact and Extended Populations
• H_alpha Emission from High-Velocity Clouds and their Distances
• Fuel Efficient Galaxies: Sustaining Star Formation with Stellar Mass Loss
• Gas Rich Dwarf Spheroidals
• The EAGLE simulations: atomic hydrogen associated with galaxies
• A simple model for the evolution of disc galaxies: The Milky Way
• A Reservoir of Ionized Gas in the Galactic Halo to Sustain Star Formation in the Milky Way
• Complex C: A Low-Metallicity High-Velocity Cloud Plunging into the Milky Way
• The WSRT wide-field HI survey: II. Local Group features
• Cooling flows within galactic haloes: the kinematics and properties of infalling multi-phase gas
• ALFALFA Discovery of the Nearby Gas-Rich Dwarf Galaxy Leo P. I. HI Observations
• Chandra Detection of the First X-ray Forest along the Line of Sight To Mkn 421
• Atomic Hydrogen Gas in Dark-Matter Minihalos and the Compact High Velocity Clouds
• Highly Ionized Gas Surrounding High Velocity Cloud Complex C
• Supernova-driven gas accretion in the Milky Way
• The Population of Weak MgII Absorbers. II The Properties of Single-Cloud Systems
• Milky Way vs Andromeda: a tale of two disks
• Evidence for the Hierarchical Formation of the Galactic Spheroid
• Structure Formation With a Long-Range Scalar Dark Matter Interaction
• Massive Coronae of Galaxies
• Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy
• A Large Reservoir of Ionized Gas in the Galactic Halo: Ionized Silicon in High-Velocity and Intermediate-Velocity Clouds
• An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way's circumgalactic medium and the Local Group
• Smith's Cloud: A High-velocity Cloud Colliding with the Milky Way
• Formation of the Galactic stellar halo I. Structure and kinematics
• Ursa Major: a missing low-mass CDM halo?
• High-velocity clouds as streams of ionized and neutral gas in the halo of the Milky Way
• A Search for Very Extended Ionized Gas in Nearby Starburst and Active Galaxies
• Effects of episodic gas infall on the chemical abundances in galaxies
• The Kinematics of Intermediate Redshift Mg II Absorbers
• Diffuse X-Ray Emission from Late-Type Galaxy Haloes
• A confirmed location in the Galactic halo for the high-velocity cloud 'chain A'
• Highly Ionized High Velocity Clouds: Intergalactic Gas in the Local Group or Distant Gas in the Galactic Halo?
• Westerbork HI observations of high-velocity clouds near M31 and M33
• FUSE Observations of Atomic Abundances and Molecular Hydrogen in the Leading Arm of the Magellanic Stream
• The Evolution of Stellar Exponential Discs
• Where are the high velocity clouds?
• A Catalog of Ultra-compact High Velocity Clouds from the ALFALFA Survey: Local Group Galaxy Candidates?
• A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey
• The mode of gas accretion onto star-forming galaxies
• A Survey of FUSE and HST Sightlines through High-Velocity Cloud Complex C
• A Broad Search for Counterrotating Gas and Stars: Evidence for Mergers and Accretion
• A multi-beam HI survey of the Virgo Cluster - two isolated HI clouds ?
• Highly Ionized High-Velocity Clouds: Hot Intergalactic Medium or Galactic Halo?
• The Galactic Nature of High Velocity Cloud Complex WB
• Origin and Evolution of the Abundance Gradient along the Milky Way Disk
• Generation of galactic disc warps due to intergalactic accretion flows onto the disc
• Highly Ionized High-Velocity Clouds toward PKS 2155-304 and Markarian 509
• The properties of "dark" ΛCDM halos in the Local Group
• ALFALFA Discovery of the Nearby Gas-Rich Dwarf Galaxy Leo~P. II. Optical Imaging Observations
• Gas Accretion as a Dominant Formation Mode in Massive Galaxies from the GOODS NICMOS Survey
• An all-sky study of compact, isolated high-velocity clouds
• Simulations of High-Velocity Clouds. I. Hydrodynamics and High-Velocity High Ions
• High-Redshift Galaxy Outflows and the Formation of Dwarf Galaxies
• Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo
• A Very Sensitive 21cm Survey for Galactic High-Velocity HI
• The Structure of the Outer Halo of the Galaxy and its Relationship to Nearby Large-Scale Structure
• Hydrodynamical simulations of Galactic fountains I: evolution of single fountains
• Ongoing Galactic Accretion: Simulations and Observations of Condensed Gas in Hot Halos
• An automated search for high-velocity clouds in the Leiden/Dwingeloo Survey
• A Targeted Survey for HI Clouds in Galaxy Groups
• First Detection of Cosmic Structure in the 21-cm Intensity Field
• Galactic fountains and their connection with high and intermediate velocity clouds
• The High Velocity Gas toward Messier 5: Tracing Feedback Flows in the Inner Galaxy
• The evolution of interstellar clouds in a streaming hot plasma including heat conduction
• Deep H I observations of the compact high-velocity cloud HVC125+41-207
• Hubble Space Telescope Survey of Interstellar High-Velocity Si III
• Substructure around M31 : Evolution and Effects
• The Magellanic Stream and the density of coronal gas in the Galactic halo
• WIMP searches with gamma rays in the Fermi era: challenges, methods and results
• Highly Ionized Gas in the Galactic Halo and the High Velocity Clouds Toward PG 1116+215
• Extragalactic HI Surveys
• A Na I Absorption Map of the Small-Scale Structure in the Interstellar Gas Toward M15
• An HI survey of six Local Group analogs: I. Survey description and the search for high-velocity clouds
• The Influence of Galactic Outflows on the Formation of Nearby Dwarf Galaxies
• Where are the High Velocity Clouds in Local Group Analogs?
• Are Newly Discovered HI High Velocity Clouds Minihalos in the Local Group?
• Late Gas accretion onto Primordial Minihalos: a Model for Leo T, Dark Galaxies and Extragalactic High-Velocity Clouds
• A blind HI survey in the Canes Venatici region
• WHAM Observations of H-alpha from High-Velocity Clouds: Are They Galactic or Extragalactic?
• Fermi-LAT Observations of Gamma-Ray Emission Towards the Outer Halo of M31
• How runaway stars boost galactic outflows
• Intermediate- and high-velocity clouds in the Milky Way I: covering factors and vertical heights
• Cold gas accretion by high-velocity clouds and their connection to QSO absorption-line systems
• The Chemical Evolution of the Galaxy with Variable IMFs
• High-resolution imaging of compact high-velocity clouds (II)
• The Role of Heating and Enrichment in Galaxy Formation
• Are Compact High-Velocity Clouds Extragalactic Objects?
• HI clouds in the proximity of M33
• Two-Dimensional MHD Numerical Simulations of Magnetic Reconnection Triggered by A Supernova Shock in Interstellar Medium, Generation of X-Ray Gas in Galaxy
• The Low Surface Brightness Extent of the Fornax Cluster
• The Arecibo Legacy Fast ALFA Survey: V. HI Source Catalog of the Anti-Virgo Region at dec=27 degrees
• Relics of structure formation: extra-planar gas and high-velocity clouds around the Andromeda Galaxy
• The Space Density of Primordial Gas Clouds near Galaxies and Groups and their Relation to Galactic HVCs
• A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies
• High Velocity Cloud Complex H: A Satellite of the Milky Way in a Retrograde Orbit?
• The Smith Cloud: high-velocity accretion and dark-matter confinement
• Very Metal-Poor Outer-Halo Stars with Round Orbits
• The Absence of Stars in Compact High-Velocity Clouds
• Lyman Limit Systems in Cosmological Simulations
• An absorption-selected survey of neutral gas in the Milky Way halo
• Dark Matter Interpretation of the Fermi-LAT Observations Toward the Outer Halo of M31
• Ultra-Compact High Velocity Clouds as Minihalos and Dwarf Galaxies
• An HI survey of the Centaurus and Sculptor Groups - Constraints on the space density of low mass galaxies
• The red stellar population in NGC 1569
• A Limit on the Metallicity of Compact High Velocity Clouds
• High-Velocity Clouds and the Local Intergalactic Medium
• The role of gas infall in the evolution of disc galaxies
• Arecibo imaging of compact high-velocity clouds
• Effelsberg HI observations of compact high-velocity clouds
• Magnetized Gas in the Smith High Velocity Cloud
• Modelling Galaxies with a 3d Multi-Phase ISM
• Dynamical and chemical evolution of NGC1569
• Molecular hydrogen beyond the optical edge of an isolated spiral galaxy
• The Smith Cloud and its dark matter halo: Survival of a Galactic disc passage
• Tidal truncation of gas replenishment and global suppression of galactic star formation in distant clusters
• The high-velocity clouds and the Magellanic Clouds
• High-Velocity Clouds in the Nearby Spiral Galaxy M 83
• A Dynamical Model for the Orbit of the Andromeda Galaxy M31 and the Origin of the Local Group of Galaxies
• Adaptive Mesh Refinement Simulations of the Ionization Structure and Kinematics of Damped Ly$\alpha$ Systems with Self-consistent Radiative Transfer
• Origin(s) of the Highly Ionized High-Velocity Clouds Based on Their Distances
• Gas Accretion onto the Milky Way
• Interstellar and Circumstellar Optical & Ultraviolet Lines Towards SN1998S
• Energy Dissipation in Multi-Phase Infalling Clouds in Galaxy Halos
• Morphological Evolution of Dwarf Galaxies in the Local Group
• Gravitational Quenching by Clumpy Accretion in Cool Core Clusters: Convective Dynamical Response to Overheating
• Anomalous HI in NGC 2997
• Absorption Line Study of Halo Gas in NGC 3067 Toward the Background Quasar 3C 232
• The Milky Way halo as a QSO absorption-line system. New results from an HST/STIS absorption-line catalogue of Galactic high-velocity clouds
• Sensitive 21cm Observations of Neutral Hydrogen in the Local Group near M31
• The Evolved Red Stellar Content of M32
• The Cosmological Significance of High-Velocity Cloud Complex H
• The Evolution of Gas Clouds Falling in the Magnetized Galactic Halo: High Velocity Clouds (HVCs) Originated in the Galactic Fountain
• SDSS Survey for Resolved Milky Way Satellite Galaxies II: High-Velocity Clouds in the Early Data Release
• GASS High Velocity Clouds in the Region of the Magellanic Leading Arm
• Magnetized High Velocity Clouds in the Galactic Halo: A New Distance Constraint
• Collisions between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud
• Decaying Dark Matter and the Deficit of Dwarf Haloes
• Warm Gas and Ionizing Photons in the Local Group (ApJL version)
• Photoionized OVI absorbers toward the bright QSO HE 0515-4414
• Galaxy Evolution in Local Group Analogs. I. A GALEX study of nearby groups
• The Arecibo Galaxy Environment Survey X: The Structure of Halo Gas Around M33
• QSO Absorption Line Constraints on Intragroup High-Velocity Clouds
• Discovery of Star Formation in the Extreme Outer Galaxy Possibly Induced by a High-velocity Cloud Impact
• ORFEUS echelle spectra: Molecular hydrogen in disk, IVC, and HVC gas in front of the LMC
• HI Observations of an Ultra-Compact High-Velocity Cloud
• Constraints of the Clumpyness of Dark Matter Halos Through Heating of the Disk Galaxies
• AGC198606: A gas-bearing dark matter minihalo?
• Status of HI searches for CHVCs beyond the Local Group
• Observations of the Extended Distribution of Ionized Hydrogen in the Plane of M31
• Physical properties of two compact high-velocity clouds possibly associated with the Leading Arm of the Magellanic System
• A Search for Stellar Populations in High Velocity Clouds
• Searching for Stars in Compact High-Velocity Clouds. I First Results from VLT and 2MASS
• Photoionized Gas in Dark-Matter Minihalos in the Galactic Halo and Local Group
• The Failure of Self-Interacting Dark Matter to solve the Overabundance of Dark Satellites and the Soft Core Question
• A survey of HI gas toward the Andromeda Galaxy
• Structual Study of Galactic Hot Gas toward Markarian 421 from X-Ray Absorption and Emission Lines
• Exploring the Dust Content of Galactic Halos with Herschel III. NGC 891
• How can star formation be sustained?
• Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud
• X-Ray Searches for Emission from the WHIM in the Galactic Halo and the Intergalactic Medium
• On the origin of anomalous velocity clouds in the Milky Way
• A Search For Star Formation in the Smith Cloud
• The Search for Intergalactic Hydrogen Clouds in Voids
• Attack of the Flying Snakes : Formation of Isolated HI Clouds By Fragmentation of Long Streams
• Multiwavelength Campaign on Mrk 509 X. Lower limit on the distance of the absorber from HST COS and STIS spectroscopy
• Multiwavelength campaign on Mrk 509 IX. The Galactic foreground
• Detection of an Optical Counterpart to the ALFALFA Ultra-compact High Velocity Cloud AGC 249525
• Probing Primordial and Pre-Galactic Lithium with High Velocity Clouds
• The contribution of halo red giant mass loss to the high-velocity gas falling onto the Milky Way disk
• A search for intergalactic HI gas in the NGC 1808 group of galaxies
• New detections of embedded clusters in the Galactic halo
• Searching for the Intra-Group Medium in Loose Groups of Galaxies
• Searching for Stars in Compact High-Velocity Clouds. II
• A 5deg x 5deg deep HI survey of the M81 group
• Faint HI 21-cm Emission Line Wings at Forbidden-Velocities
• Understanding dwarf galaxies as galactic building blocks
• HI Clouds in the M81 Filament as Dark Matter Minihalos--A Phase-Space Mismatch
• High-energy radiation from collisions of high velocity clouds and the Galactic disk
• Neutral hydrogen in galactic fountains
• Do High-Velocity Clouds trace the Dark Matter subhalo population?
• A High-Metallicity High Velocity Cloud along the MRK 421 Sight Line: A Tracer of Complex M?
• The gaseous extent of galaxies and the origin of Lyman alpha absorption systems. IV: Lyman alpha absorbers arising in a galaxy group
• Interaction of galactic wind with halo gas and the origin of multiphase extraplanar material
• The Distance and Properties of Hydrogen Clouds in the Leading Arm of the Magellanic System
• Multiwavelength observations of the M15 intermediate velocity cloud
• HI observations of three compact high-velocity clouds around the Milky Way
• Galaxy Selection and Clustering and Lyman alpha Absorber Identification
• CaII K interstellar observations towards early disc and halostars - Paper II; distances to IVCs and HVCs
• Large and small-scale structure of the Intermediate and High Velocity Clouds towards the LMC and SMC
• Molecular gas in high-velocity clouds: revisited scenario
• Modeling the Void H I Column Density Spectrum
• Evaporation and Condensation Processes of Giant Molecular Clouds in a Hot Plasma
• Global properties of the HI high velocity sky, a statistical investigation based on the LAB survey
• A population of high-velocity absorption-line systems residing in the Local Group
• Low Redshift QSO Lyman alpha Absorption Line Systems Associated with Galaxies
• The Nature and Origin of the Non-Void Lyman alpha Cloud Population
• The Properties of Satellite Galaxies in External Systems. I. Morphology and Structural Parameters
• Synchrotron Emission from Dark Matter in Galactic Subhalos. A Look into the Smith Cloud
• Mini High Velocity Clouds
• Is High-Velocity Cloud Complex C Associated with the Galactic Warp?
• The Accretion of Lyman Alplha Clouds onto Gas-Rech Protogalaxies; A Scenario for the Formation of Globular Star Clusters
• A 5deg x 5deg deep HI survey of the M81 group: II. HI distribution and kinematics of IC 2574 and HIJASS J1021+68
• Secular evolution versus hierarchical merging: galaxy evolution along the Hubble sequence, in the field and rich environments
• Low and high velocity clouds produced by young stellar clusters
• First Detection of Molecular Gas in the Giant Low Surface Brightness Galaxy Malin 1
• Optical spectroscopy of the M15 intermediate velocity cloud
• The Nature of a Dusty Ring in Virgo
• A new delivery route to Galactic Nuclei: Warm halo cloud impacts
• New evidence for halo gas accretion onto disk galaxies
• Detecting Dark Matter in High Velocity Clouds
• An Intermediate Velocity HI Cloud Falling to the Galactic Disk; Possible Evidence for Low Metallicity HI Gas Originated Outside the Galactic Disk
• Solar-Metallicity Gas in the Extended Halo of a Galaxy at $z\sim 0.12$
• Bar-driven injection of intergalactic matter into galactic halos
• The Kinetic Sunyaev-Zel'dovich effect of the Milky Way Halo
• High Velocity Cloud Edges and Mini-HVCs
• Do the Unidentified EGRET Sources Trace Annihilating Dark Matter in the Local Group?
• Accretion Onto the Milky Way: The Smith Cloud
• Neutral Gas Accretion onto Nearby Galaxies
• Studying Galaxy Formation in Loose Galaxy Groups
• Gas flows, star formation and galaxy evolution
• Search for dark matter in compact hydrogen clouds
• AAT/WFI observations of the Extragalactic H I Cloud HIPASS J1712-64
• Estimating the Fuel Supply Rate on the Galactic Disk from High Velocity Clouds (HVCs) Infall
• The Baryonic Mass Estimates of the Milky Way Halo in the form of High Velocity Clouds
• The HI Detection of Low Column Density Clouds and Galaxies
• A Catalogue of Field Horizontal Branch Stars Aligned with High Velocity Clouds
• Searching for an Intrinsic Stellar Population in Compact High-Velocity Clouds
• HI and Galaxy Formation in Loose Groups
• Scale-dependent Energy Transfer Rate as a Tracer for Star Formation in Cosmological N-Body Simulations
• Scale Interactions and Galaxy Evolution
• HI in Local Group analogs: what does it tell us about galaxy formation?
• Compact High-Velocity Clouds at High Resolution
• Substructures in Minor Mergers' Tidal Streams
• The Maximum Effect of Thermal Instability on Galactic Outflows